This invention relates to an image printing device in which desired images represented by two or more valued data are recorded with a laser.
Recently, methods of printing images with a laser, and apparatuses for practicing the methods have been actively developed, and a number of patent applications have been filed therefor. Among those patent applications, Japanese Patent Application (OPI) No 291184/1986 should be taken into consideration (the term "OPI" as used herein means an "unexamined published application").
FIG. 1 is a diagram outlining the laser printing method disclosed by the above mentioned Japanese Patent Application. In FIG. 1, reference numeral 101 designates a support; 102, a heat generating layer; 103, a leuco dye layer; 104, a developer-contained image receiving layer; 105, an image receiving base; and, 100, a laser beam converged to have a predetermined beam diameter and intensity-modulated according to the image signal. The support 101, the heat generating layer 102 and the dye layer 103 form a transferring sheet 300. The image receiving layer 104 and the image receiving base 105 form an image receiving sheet 400.
The coloring operation thereof will be described. The laser beam 100, which has been intensity-modulated according to the image signal and converged to have a predetermined beam diameter is applied through the support 101 made of a transparent film to the heat generating layer 102. As a result, the heat generating layer 102 generates heat through light absorption according to the energy of the laser beam 100. The dye of the leuco dye layer 103 is transferred over to the developer-contained image receiving layer 103 of the image receiving sheet by the heat thus generated. The dye and the developer react with each other, thus coloring, as a result of which the image is formed. This operation is continuously carried out to obtain a two-dimensional recorded image.
The coloring operation is as outlined above. The apparatus further includes: laser beam scanning device; laser beam modulating means, memory device for storing image signals to be modulated device for abutting the transferring sheet and the image receiving against each other, device for conveying these sheets and device for synchronizing the operations of the device described above. The apparatus has been disclosed, for instance, by Japanese Patent Application (OPI) No's 8949/1976, 128277/1987, 159973/1987, and 108669/1987.
The conventional image printing method using a laser is as described above. That is, the generation of heat depends fully on the energy of the laser beam. Therefore, the conventional method suffers from a problem that an expensive high-power laser must be employed. For instance, the laser output 0.5 W described in the specification of the above-described Japanese Patent Application (Laser Printing Method) is 100 times as high as the output 5 mW of a semiconductor laser which is most generally employed for compact disc players or the like. In addition, it is expensive, and is relatively short in service life.